Colloquial male speech for 'my house' or 'my place' (shortened from 俺のうち); very casual and typically used by men.
今夜、俺んちで映画を見ようぜ。
Let's watch a movie at my place tonight.
仕事が終わったら俺んちに寄っていいよ。
You can stop by my place after work.
俺んちの犬はすごく人懐っこい。
The dog at my place is very friendly.